1. Field of the Invention
The present invention relates to a flexible coupling for a rotary drive transmission used on an automobile propeller shaft and the like.
2. Description of the Present Art
A commonly known conventional flexible coupling is a coupling which has an elastic body by which an inner tube and an outer tube are connected in the diametrical direction, and through this flexible body a rotary drive force is transmitted with pliant elastic distortion in the direction of the shaft and some degree of elastic distortion in the direction of rotation.
An example of such a conventional flexible coupling is the coupling illustrated on page 4 of "KE COUPLING" published in June 1983 by Kawasaki Heavy Industries, Ltd.
However, in such a conventional flexible coupling, if even a certain degree of elastic distortion is possible in the direction of rotation, since there is no damping effect there is a large resonance created in the rear suspension system, giving rise to the problem that the comfort in the vehicle is worsened.
For example, in a six cylinder automobile, when the engine is rotating at 3000 RPM, about 150 Hz of vibration is transmitted through the propeller shaft to the rear suspension, and if this frequency becomes the same as the resonant frequency of the rear suspension system, the rear axle vibrates severely in the front and rear direction of the vehicle from the resonance phenomenon.
This front to rear vibration, passing through the differential gear, becomes a vibration in the direction of rotation, and is transmitted to the propeller shaft. In a conventional flexible coupling this vibration cannot be damped, so that the sound vibration performance of the vehicle is worsened.